Handover is a process where the support of a radio connection with a mobile radio station is “handed over” from a source cell currently supporting the radio connection to another target cell. Often, such a handover is done because the mobile is moving away from the source cell's base station towards the target cell's base station. Different types of handovers are possible such as a hard handover (sometimes described as “break-before-make”), a soft handover (sometimes described as “make-before-break”), or a softer handover (soft handover between sector cells controlled by the same base station). Sometimes handover attempts fail, and the question is what happens to the connection. In a worst case situation, the connection is dropped, which requires the user to reinitiate the radio connection. A best case is where the source base station continues to support the connection.
In some cellular systems, mobile connections are supported using shared radio resources, e.g., a shared channel. A shared channel can be more efficiently operated then a dedicated channel. But shared channels require some way to regulate access to the shared resources. For an uplink shared channel, for example, mobiles can be scheduled for uplink transmission, or random access attempts to acquire uplink transmission resources can be regulated using some sort of contention resolution procedure. In either situation, when there is a failed handover attempt for a radio connection on a shared channel, there will likely be some delay as the mobile station must compete, often times in a random access process, with other mobile stations to reacquire uplink resources to support its radio connection. That delay can be substantial depending on the demand for radio resources in that source cell at the time. Indeed, in an example contention-based random access procedure, the mobile station might randomly select the same random access preamble (a known bit sequence used in the random access procedure) as one or more other mobile stations trying to establish a connection in the source cell, lose the contention for radio resources at the end of the random access process even if different preambles are selected, and be forced to restart such a random access procedure. In any event, it would be desirable to avoid these types of delays resulting from a failed handover so that there is no significant interruption in service.